Experimental Study On Shear Strength Of RC Frame Joint Strengthened By Prestressed Closed Wire Rope Units

A new technology of strengthening RC beam-column joints was developed in this study against the problems of the traditional node reinforcement technology. Transverse prestressing was put to the steel wire ropes in the joint core with effective end anchorage to achieve the active constraint in transverse direction and improve the ultimate bearing capacity and deformation properties of core concrete. In this way, the mechanical performance of frame nodes was improved. The following research was carried out, based on the former work of the project team.Firstly, deep optimizations was made against the problems of the traditional node reinforcement technology by setting up specific construction and control technology.Second, four methods to calculate the shear strength of RC joints prescribed by ACI318-05, AIJ, NZS3101, GB5001-2010 were introduced. The results indicate that the ACI specification dosen’t consider the positive factors of the axial force and orthogonal beam space constraint, and the shear strength calculation is relatively conservative which lead to the high safety reserve; the AIJ calculation of all kinds of joint shear is larger, which tends to be dangerous; the NZS considered the effect of restraint space node, but it provides a conservative calculation results, especially for the space joint; According to the GB5001-2010, the numerical are in good agreement with the experimental values for different joint types with lower safety margin than the ACI and NZS.Additionally, six RC frames reinforced with prestressed steel wire ropes were tested to investigate the influence of the ratio of the steel wire ropes, prestress level and mortar to the shear performance of the node of reinforcement. The results show that:(1) The integral seismic performance improved obviously. The energy dissipation, ductility and pinching effect got improved significantly as the axial compression ratio increases.(2) The transverse prestressing can effectively reduce the hysteresis effect. The concrete cracking was put off and the proportion of the displacement angle caused by shear deformation was reduced as the prestress level increased.(3) At the beginning of the loading, the mortar was benefit to the stiffness by resisting shear together with the core concrete. When shear deformation of the node increased, the polymer mortar cracked and gradually quit the job, so the mortar have little meaning to the hysteretic energy dissipation performance and the ultimate bearing capacity.Finally, combining with the reinforced concrete frame node "oblique compression bar- truss" stress mechanism, analysis of the shear stress after reinforcement mechanism. Is derived based on the superposition principle, strengthening the shear formula of ultimate shear capacity, and will get the shear bearing capacity test of test value and the derived formula, comparing the calculated values calculated results coincide well.